1. Field of the Invention
The present invention relates to a variable displacement scroll compressor.
2. Description of Related Art
In a case of a known prior art scroll compressor, a stationary scroll and an orbiting scroll contact with each other, and refrigerant is compressed in each of two closed spaces (compression chambers), which are defined between the stationary scroll and the orbiting scroll. In this scroll compressor, the orbiting scroll revolves multiple times (e.g., twice) relative to the stationary scroll, so that the refrigerant, which is drawn into each of the compression chamber, is compressed. In comparison to a reciprocal compressor, the compression of the refrigerant is moderate in the scroll compressor, and thereby leakage of the refrigerant from each compression chamber is small in the scroll compressor.
One such a scroll compressor is known as a variable displacement scroll compressor (see, for example, JPS59-028083A, which corresponds to U.S. Pat. No. 4,505,651A). In the known variable displacement compressor, two bypass holes are symmetrically placed about a rotational center (also referred to as an orbital center or a revolution center) of the orbiting scroll, about which the orbiting scroll revolves relative to the stationary scroll. During a compression stroke for compressing the refrigerant, the refrigerant of each of the two compression chambers, which are formed through the contact between the stationary scroll and the orbiting scroll, is returned to a suction chamber through the corresponding one of the two bypass holes, so that a displacement (i.e., a volume of refrigerant, which is displaced, i.e., discharged per cycle) is changed, i.e., is varied. The two compression chambers are formed as closed spaces and are placed on one side and the other side, respectively, of a winding center of the scrolls. Specifically, one of the two compression chambers is defined by an inner peripheral wall surface of the stationary scroll (more specifically, a stationary wrap of the stationary scroll) and an outer peripheral wall surface of the orbiting scroll (more specifically, an orbiting wrap of the orbiting scroll), and the other one of the two compression chambers is defined between an outer peripheral wall surface of the stationary scroll and an inner peripheral wall surface of the orbiting scroll.
As in the case of the variable displacement scroll compressor of JPS59-028083A (corresponds to U.S. Pat. No. 4,505,651A), in which the two bypass holes are symmetrically placed about the rotational center of the orbiting scroll, the refrigerant of the one compression chamber and the refrigerant of the other compression chamber are returned to the suction chamber through the two bypass holes, respectively, at the same timing. Thereby, a compression stroke (a compression process or a compression period) of the compressor is shortened, and thereby the number of turns of the winding of each scroll is actually reduced.
For example, in a case of the variable displacement scroll compressor, in which the orbiting scroll revolves twice to compress the refrigerant drawn into the corresponding compression chamber at the time of operating the compressor at a maximum displacement (100% displacement), i.e., at a maximum displacement operational mode, when this variable displacement scroll compressor is operated at a variable displacement, i.e., at a variable displacement operational mode, the orbiting scroll may revolve once to compress and discharge the drawn refrigerant. Therefore, in the variable displacement operational mode, the compression stroke (the compression process or the compression period) of the compressor for compressing the fluid, i.e., the refrigerant is reduced.
In such a variable displacement scroll compressor, the compression of the refrigerant at the variable displacement operational mode is not moderate (i.e., is rapid), and thereby the refrigerant of each compression chamber may possibly leak from the compression chamber to result in a reduction in compression efficiency of the compressor at the time of operating the compressor at the variable displacement operational mode.